FIG. 12 shows a structure of a conventional MI element (Patent Document 1).
In an MI element 9, an amorphous wire 92 is fixed to a center portion on a substrate 91, and a detecting coil 93 is wound around a periphery of the substrate. An amorphous wire having a length of 4 mm and a diameter of 30 μm is used as the amorphous wire 92, and a width of 3 mm, a height of 2 mm, and a length of 4 mm are generally set as dimensions of the MI element.
When the conventional MI element is applied as a magnetic sensor, the MI element achieves high sensitivity and a size-reduction to some extent. However, the MI element is not always sufficient as a high-performance magnetic sensor (to be referred to as an MI sensor hereinafter).
Since an amorphous wire serving as a magnetic core of an MI element is crystallized in solder connection by heating, electrical connection by ultrasonic bonding or the like is performed between both the ends of the amorphous wire and electrodes. Since both the ends of the amorphous wire require the electrical connecting portions, the amorphous wire becomes long.
Since the magnetic characteristics of the amorphous wire are easily influenced by distortion due to the external stress, the amorphous wire is covered with a gelatinous material. A detecting coil becomes thick because the coil has a structure in which the amorphous wire covered with the gelatinous material on a substrate and the substrate are wound outer peripherally.
For this reason, the MI element has a large size, and is difficult to be reduced in size.    Patent Document 1: Japanese Unexamined Patent Publication No. 2001-296127
In order to reduce the size of an MI element, an amorphous wire itself needs to be shortened, and a detecting coil needs to be wound only around an amorphous wire without outer peripheral winding of a substrate. However, a stress-free amorphous wire is difficult to be arranged on a detecting coil pattern on the substrate. When stress acts on an amorphous wire, the magnetic characteristics of the amorphous wire are influenced, and an MI effect cannot be sufficiently exerted. For this reason, the reliability of an MI element is deteriorated.
Thus, when a groove is formed in the substrate to bury an amorphous wire in the groove, any stress does not act on the amorphous wire, and a reliable MI element is expected.
FIGS. 13 and 14 show a structure (recessed type) of a groove type MI element (Patent Document 2).
A groove type MI element obtained by microfabrication achieves a considerable size-reduction of the conventional MI element. In the structure, an extending groove 11 (recessed shape) is formed in a certain direction on a substrate 1 by a cutting process, an amorphous wire 2, an insulator 4, and a first detecting coil unit 31 are buried in the extending groove, and a second detecting coil unit 32 is formed on a groove upper surface 112. In this manner, an amorphous wire having a length of 1.5 mm and a diameter of 30 μm is used as the amorphous wire 2, and dimensions of the substrate 1 are a width of 0.5 mm, a thickness (height) of 0.5 mm, and a length of 1.5 mm. The groove on the substrate has a depth of 0.05 mm and a width of 0.07 mm.
However, since an extending groove forming is performed in the substrate, the MI element having the groove type structure (recessed type) may be damaged in the extending groove forming. A current amorphous wire has 30 μm, and an output from a detecting coil increases when the detecting coil is proximally wound as much as possible. For this reason, the width of a blade for forming the groove is preferably close to 30 μm as much as possible.
However, the width of a normal blade used in forming the groove of ceramic is 100 μm or more. A size smaller than 100 μm is a special size, and 50 μm is a minimum grade. For this reason, in the current process, a groove is formed with a blade having a width of a minimum grade of 50 to 70 μm. However, when the blade width decreases, the blade may be worn out and damaged.
In particular, at a wafer serving as a base material of a substrate on which a wire is mounted, if a widely-used alumina ceramic substrate is used, and the groove is formed at a processing speed on industrial standards with the blade having the above width, both the blade and the wafer are cracked.
For this reason, in order to process the wafer without being cracked, the wafer needs to be slowly processed regardless of productivity. Therefore, in fact, a machinable ceramic softer than normal alumina must be used as a material of a ceramic substrate for a wafer.
A groove depth minimally requires a depth obtained by adding about 15 μm to a wire diameter to cover the wire with an insulating layer and a coil, and a groove depth requires about 50 μm when a 30 μm-wire is used. In a groove structure having a groove width of 50 μm and a groove depth of 50 μm, a thickness of an entire substrate requires about 0.6 mm to prevent the substrate from being cracked by a groove. The reason of the requirement is that a current product uses machinable ceramic having good processability and low strength. Even though the machinable ceramic is used, a groove-forming blade is rapidly worn out because a blade width of the groove-forming blade is narrow. This resulted in increase of a cost
In addition, when the groove depth of the substrate is deepened to 50 μm or more, a notch effect of the groove to the substrate becomes large to deteriorate substrate strength, and the substrate needs to be increased in thickness and size.
More specifically, when a groove structure of a 30-μm-diameter wire are used, the groove structure has a groove width ranging from 50 to 70 μm, a groove depth of 50 μm, and a substrate thickness of 0.6 mm, and it is optimized in terms of an output characteristic and a reduction in size.
In the extending groove structure, the groove structure is tried to be reduced in size to further reduce an entire element in size. However, the size reduction of the groove structure is difficult because the groove width cannot be 50 μm or less due to a limitation of the size of the blade.
Even if the groove width is fixed to 50 μm, a groove depth may be reduced by narrowing a wire diameter to reduce a notch effect and allow a substrate to be thinner.
In a groove structure, a detecting coil is formed along a groove. For this reason, even though a wire diameter is small, a detecting coil has 50 μm in a groove width direction and a wire diameter+about 15 μm in a depth direction because a groove width is fixed. When the wire diameter decreases, a proximal winding cannot be obtained. For this reason, an output characteristic of an MI element reduces considerably more than a reduction in diameter because a wire diameter reduces to relatively separate the detecting coil from a wire diameter.
When the wire diameter is small with reference to a groove width, a wire is difficult to be located at the center of a detecting coil. For this reason, an output characteristic fluctuates due to a fluctuation in wire position.
Furthermore, the machinable ceramic is difficult to be thinly processed in a depth direction, and a processing speed needs to be slow, so that an edge of the blade is intensively worn out. For this reason, a groove shape in a wafer fluctuates. When an insulating layer made of a resin or the like is supplied on the basis of the same shape, a problem such that the resin overflows the groove is posed, and the productivity is seriously deteriorated.
As described above, a reduction in size, especially, a reduction in thickness of the substrate cannot easily be achieved while satisfying both retention of strength during such as in processing and assembling an MI element in a substrate groove in this groove structure scheme, and maintenance of the output characteristic of the MI element.
A material of the substrate is limited to a material having good cutting performance such as a machinable ceramic to form an extending groove, and a size of a wafer used is also limited.    Patent Document 2: Domestic Re-publication of PCT International Publication for Patent Application: WO2003/071299
On the other hand, an MI element formed of an amorphous wire is not suitable for microfabrication. An ultra-compact magnetic detecting element is difficult to be formed because coil winding and amounting will be cumbersome. For this reason, an MI element in which a thin-film magnetic core is formed on a substrate is proposed (Patent Document 3 and Patent Document 4).
The thin film magnetic core itself will not be a stress since the core is formed of a sputtering film on the substrate. Therefore, the MI element formed of a thin film magnetic core is easily arranged.
However, in comparison with an MI element using an amorphous wire having a circular sectional shape, the MI element using a thin film magnetic core having a rectangular film shape in cross section cannot sufficiently exert a magnetic impedance effect in a width direction of the rectangular film.    Patent Document 3: Japanese Unexamined Patent Publication No. 2000-292506    Patent Document 4: Japanese Unexamined Patent Publication No. 2002-270918